VARIATION AND HEREDITY 225 



plants were of two classes. Some of them were tall 

 and some dwarf, like the original, in the approximate 

 proportion of three of the former to one of the latter. 

 Again self-fertilizing the flowers on the various plants, 

 he found that the seeds from the dwarf plants 

 developed dwarfs, and this was repeated in subse- 

 quent generations, whereas some of the tall plants 

 developed only tails (i.e. " bred true "), and others 



TALLfPure) X DWARF 



TALL r- 



(Impunej ""M 



! L 



ire, 



DWARF t 



Ratio 3't (277) "~Ml 



'WARF- F^ 



PURE'TALL IMPURE TALL 



^ Ratio l.l^'W^ 



FIG. 80. Diagram of the ratios obtained by Mendel in crossing tall peas 

 with dwarf. (Punnett.) 



developed both tails and dwarfs, again in the ratio of 

 three to one. 



Two important facts are brought out in this ex- 

 periment. First, the characters " tallness " and 

 " dwarf ness," whatever their predetermining cause 1 

 may be, exist in the gametes as segregate entities, 

 sorting out in mathematical ratios in each generation. 

 To such, the name " unit characters " has been 



1 "Tallness" in peas differs from tallness in human beings in that it 

 depends upon the characteristic length of internode between the joints 

 where the leaves are given off, i.e. the dwarf pea is not a miniature pea 

 but a different kind of a pea with regard to this one character. 

 Q 



